This invention relates to an apparatus for measuring the autofluorescence of the cornea of an eye, comprising means for substantially tangentially illuminating the cornea, means for receiving the autofluorescent radiation generated in the cornea by this illumination, and means for processing the measured autofluorescent radiation.
Such an apparatus is known from Italian patent application IT-94.501.069.
Apparatuses for measuring the autofluorescent radiation of the cornea of an eye are used in screening diabetes patients for diabetic retinopathy. Diabetic retinopathy is one of the moat important causes of blindness in the Western world and its timely detection can contribute to delaying or even preventing blindness in patients by administering laser therapy. Recent studies have shown that the autofluorescence of the corneal tissue in certain wavelength regions increases considerably with the severity of diabetic retinopathy. By other conventional methods, diabetic retinopathy and its progression are difficult to detect. The advantage of measuring corneal autofluorescence is that the cornea is readily accessible for examination and that the amount of corneal autofluorescence is not or only slightly age-dependent.
In the apparatus known from the above-mentioned Italian patent application, the above-described insight is already utilized in an attempt to measure corneal autofluorescence. In practice, however, this known apparatus has proved to be insufficiently sensitive and accurate, inter alia because the autofluorescence of the crystalline lens located behind the cornea is many times greater than the autofluorescence of the cornea itself, so that in the absence of measures to suppress lenticular autofluorescence, the measurement is not sufficiently accurate. An additional problem is that lenticular autofluorescence is highly age-dependent, starting at near-zero at birth and increasing to 50 times the value of corneal autofluorescence at the age of 90. Further, the spread of lenticular autofluorescence among individuals of the same age is large. Accordingly, lenticular autofluorescence cannot be simply eliminated as a fixed interference factor, since its value is unknown.
The object of the invention is to improve the known apparatus, such that, in a simple and yet sufficiently accurate manner, corneal autofluorescence can be measured, while yet the apparatus is of simple and robust construction. In addition, the object of the invention is to provide an apparatus that is inexpensive to manufacture and simple to operate, which is of great importance especially for use in developing countries.
To that end, the invention provides an apparatus of the above-mentioned type, characterized in that the means for tangentially illuminating the cornea comprise at least one light source which radiates blue light and at least one filter which transmits at least a part of the blue light in a light path to the cornea, that the means for receiving the autofluorescent radiation generated in the cornea comprise at least one filter which transmits green light, that the apparatus further comprises a light source for causing the pupil to contract, as well as switching means for switching on, in succession, the blue light source for a first predetermined period and then the light source for causing the pupil to contract for a second predetermined period, and for repeating this cycle a number of times.
It is noted that EP-A-776628 discloses an apparatus for eye measurement which is alleged to make it possible to perform a variety of types of eye measurements, including measuring the autofluorescence generated by the cornea. This publication, however, is directed to measuring autofluorescence values to determine whether or not a patient has diabetes. The device described, however, is not accurate enough to determine whether in a patient diabetic retinopathy occurs, i.e., whether in a patient already known to have diabetes, the diabetes also affects the cornea. The differences in corneal autofluorescence values to be measured for this purpose are so small that the known device is not suitable for that. Moreover, the known device is large and costly, while, further, use is made of a line-shaped light ray for exciting the cornea, instead of a light beam as in the invention. Nor does the publication mentioned disclose the provision of separate light sources which keep the pupil contracted prior to measurement, but also during measurement. Only an additional light source for focusing the eye is described.
The invention will be further elucidated hereinafter on the basis of an exemplary embodiment, with reference to the drawings, wherein: